1. Field of the Invention
The present invention relates to a solenoid valve device having three fluid ports in which fluid communication among the three fluid ports is switched over.
2. Description of Related Art
In a conventional solenoid valve device, a fluid passage and three fluid ports communicating with the fluid passage are formed in a housing. Fluid communication among the three fluid ports is switched over by reciprocating movement of a valve member accommodated in the fluid passage. The conventional solenoid valve device, in which a stopper portion coming in contact with the valve member and defining a stroke of the valve member reciprocatingly movable is positioned outside the housing, has a drawback in that sounds or noises generated by the valve member hitting on the stopper portion are likely heard outside the solenoid valve device.
U.S. Pat. No. 6,163,239 discloses a solenoid valve device that is duty controlled for switching over the communication among the three fluid ports. In the solenoid valve device disclosed in U.S. Pat. No. 6,163,239, when a plunger is attracted toward a guide upon energizing a coil, the plunger rests at a position away by a certain gap from the guide so that the plunger never hits the guide. When the plunger moves in a direction of leaving the guide upon de-energizing the coil, position of the plunger away from the guide is governed by a biasing force of a spring that urges the plunger toward the guide.
When the spring defines the position of the plunger away from the guide, the position of the plunger is likely to vary for a while just after the coil is de-energized. In case of the duty controlled solenoid valve device, in particular, when a very high duty ratio becomes necessary and the coil is energized in a very short time after the coil is de-energized, the position of the plunger on energizing the coil tends to be fluctuated. This causes a drawback in that correlation between the duty ratio and output pressure does not show a linear line and is unstable, as shown in FIG. 3B.
An object of the present invention is to provide a solenoid valve device in which hitting noises are hardly heard outside.
Another object of the present invention is to provide a solenoid valve in which correlation between the duty ratio and the output pressure is stable.
To achieve the above object, a solenoid valve device for switching over communication among first, second and third fluid circuits is composed of a stator including a coil, a housing made of magnetic material and connected with the stator, a movable core, a valve seat member fixed to an inside of the housing, a movable member fixed to and movable together with the movable core, and a ball. The housing has a fluid passage formed inside, an accommodation bore whose axial end communicates with the fluid passage and whose another axial end is opened to an outer wall of the housing on a side of the stator, and first, second and third fluid ports through which the first, second and third fluid circuits communicate with the fluid passage, respectively. The housing is further provided on an inner wall of the housing forming the fluid passage around the axial end of the accommodation bore with a stopper portion. The movable core is axially opposed to and spaced from the outer wall of the housing to which the accommodation bore is opened and axially movable reciprocatingly upon energizing and de-energizing the coil. The valve seat member is fixed to an inner circumferential wall of the housing forming the fluid passage and has a through-hole through which the first fluid port is capable to communicate with the third fluid port, a communication bore through which the through-hole communicates with the second fluid port, a first valve seat formed around an axial end of the through-hole on a side of the first fluid port and a second valve seat formed around another axial end of the through-hole on a side of the third fluid port. The movable member extends axially through the accommodation bore and has a contact portion accommodated in the fluid passage between the stopper portion and the second valve seat and a rod inserted into the through-hole from a side of the contact portion with a gap between an outer circumference of the rod and an inner circumference of the through-hole. The ball is arranged on an opposite side to the contact portion with respect to the valve seat member and axially urged toward the first valve seat.
With the solenoid valve mentioned above, when the movable member moves with the movable core toward the stator, the contact portion comes in contact with and rests at the stopper portion so that the ball comes in contact with the first valve seat, which results in achieving communication between the second and third fluid ports through the through-hole and the communication bore and shutting off communication between the first and second fluid ports and communication between the first and third fluid ports. On the other hand, when the movable member moves with the movable core in a direction opposite to the stator, the contact portion comes in contact with and rests at the second valve seat so that the ball is pushed by the rod and leaves the first contact portion, which results in achieving communication between the first and second fluid ports through the through-hole and the communication bore and shutting off communication between the third and first fluid ports and communication between the third and second fluid ports.
It is preferable that the first fluid port is a fluid input port, the second fluid port is a fluid output port and the third fluid port is a fluid drain port.
Though hitting noises occur when the contact portion hits on and rests at the stopper portion or the second valve seat, the hitting noises are hardly heard outside the solenoid valve device, since stiffness of the housing is high and sounds generated in the housing are hardly heard outside the housing. Further, if a substantial part of the housing including first, second and third fluid ports is inserted into a valve body in which the first, second and third fluid circuits are formed, the hitting noises do not leak outside the solenoid valve device.
Further, when the solenoid valve device is duty controlled for switching over the communication among the first, second and third fluid ports, the contact portion of the movable member hits on and rests at the stopper portion or the second valve seat upon de-energizing the coil so that the rest position of the movable member is not fluctuated. Accordingly, the relationship between duty ratio and output pressure of the output is linear and stable.
Moreover, it is preferable that each area of the contact portion and the second valve seat in contact with the contact portion is extremely small to an extent of eliminating a substantial influence of adhesive force due to fluid viscosity between mutual contact surfaces but sufficiently large to an extent of securing allowable limited wear of the mutual contact surfaces.
In case of using the fluid whose viscosity increases with decrease of temperature, adhesive force due to fluid viscosity tends to alter a timing when the contact portion leaves the stopper portion or the second seat valve according to change of the temperature. However, since the area of the contact portion and the second valve seat in contact with the contact portion is extremely small, the timing when the contact portion leaves the stopper portion or the second seat valve is hardly influenced by change of the fluid viscosity so that the relationship between the duty ratio and the output pressure is not variable.